Identification cards are used in many areas. For example they are used as credit cards, bank cards, bank payment cards and the like in cashless payment transactions. Provided with corresponding identification features they can also be used as cards identifying their owner. As a consequence of their being widespread, they represent typical mass articles on the one hand, meaning that their production has to be simple and cost-effective, but on the other hand they have to be designed in such a fashion that they are protected against forgery and falsification to the greatest possible extent. In addition the data stored on them should be recognizable in a simple and secure fashion by both machines and people.
Identification cards are known in which information is embossed in the card in the form of relief-like characters. The relief-like characters can on the one hand be palpated by people, and on the other hand they can also serve as printing plate for transferring the information from the card onto paper.
From EP 308 904 it is known to provide a card, which can consist of PVC among other things, with surface features in different manners by differently guided laser processing. It is described in detail how foamed embossed characters are integrated in surface plateaus, planar characters are applied on a card surface by discoloration, and visually verifiable authenticity features are applied on a card surface. By using a two-layer card-surface material whose cover layer is transparent it is also possible to effect foaming and discoloration simultaneously. However, the production of such two-layer card surfaces increases the overall card production effort.
From GB 2 057 363 A and EP 0 469 982 B1 further proposals are known to produce relief structures in plastic which differ in color from the contour. According to GB 2 057 363 A a special plastic material based on a flocked foam is used, according to EP 0 469 982 B1 the foaming of a cast plastic material is to automatically yield a change in the shade of color. The first solution is too elaborate for identification cards, the second yields only small differences in color that are hard to control.
From DE 3 213 315 A1 it is known to produce tactile characters by foaming card material by means of a laser. An identification card therein consists of a plastic material or is provided with a surface layer of a plastic material which is mixed with chemical or physical propellants. The plastic layer is heated and foamed by means of a laser beam. The locally foamed areas form a relief structure on the card surface.
From EP 1 113 131 A2 it is known to produce tactile characters by embossing and to blacken the raised embossings subsequently by means of a laser. Therein the blackening can be carried out in particular exactly on the raised areas, so that a positive writing is created, or can be carried out in between, so that a negative writing is created. Due to the blackening the relief-like, embossed tactile characters are also easily visually perceivable.
The attempt to use both above-mentioned methods for producing identification cards resulted in the finding that characters in a relief structure that were foamed by means of a laser cannot easily be blackened by means of a laser in a subsequent step, or that areas of an identification card which were blackened by means of a laser lose their blackening at least partly during the subsequent foaming. So far nobody has succeeded in producing blackened characters by means of laser treatment on an inexpensive, white standard plastic material, such as for example polyester or PVC. Such characters could be produced only by preparing the surface of the identification card in a special fashion beforehand, for example by adding carbon. However, such a preparation increases the material costs and interferes with the visual appearance of the identification card, since a gray film forms on its surface. It was furthermore found that adding carbon changes the physical properties of the card material, which can make an elaborate test and acceptance procedure necessary.
It is therefore the object of the present invention to propose an identification card with a relief structure of foamed plastic and a method for its production, in which the relief structure is easily visually perceivable.